S&W Rear Sight
If you are happy with what you have, just replace the windage screw and nut. The differance in knotch width is the wider the knotch,the more daylight you see aound the front sight. I find with older eyes,it is much easier to center the front sight with more light coming around it.Whatever you choose,Brownells will most likley have it.
Millet makes a nice replacment sight that you can get with a white outline. It gives you a nice flat larger rear sight to look through. I think your 80's vintage gun is a drop in, if not, you get the one with out the hole drilled and drill it to match your frame. It's in the Brownell's catalog #60,page 340.
sigma40